Natural resources such as gas and oil can be recovered from subterranean formations using well-known techniques. In particular, thermo-thickening compounds are known to be incorporated as thickening agents in fracturing fluids, drilling fluids or completion fluids in the gas- and oilfield industry, as illustrated in documents such as EP0583814 and US2010/0206569.
Unwanted water production in association with crude oil is one of the major production difficulties for the petroleum industry, as more reservoirs become mature. Problems due to water production often decrease the economic performance of a well.
In order to reduce excessive water production, it is known to inject, in injection and production wells, a gelling system made of a water-soluble polymer and a cross-linking agent in aqueous solution. After a sufficient time, the solution sets into a semisolid mass and behaves as a water diverting or blocking agent, while remaining permeable to oil.
It is known to use a polyacrylamide/chromium acetate system as a gelling system (Sydansk et. al., Field Testing of a New Conformance improvement Treatment Chromium (III) Gel Technology, Paper SPE 17383 presented at the SPE Enhanced Oil Recovery Symposium, Tulsa, Okla., 1988). However, the gelation time depends on the kinetics of reaction between the polymer and the cross-linking agent, whereas the reaction conditions, inside the wells, are difficult to control. Moreover, the use of chromium salts can lead to environmental pollution problems.
Another problem encountered in the oil or gas industry relates to water channelling problems between injection wells and production wells. When injected into the injection well, water may follow a preferential pathway through high-permeability streaks of the reservoir. Some oil- or gas-rich zones, of lower water permeability, remain unswept by the water flow.
Therefore, the production of such wells could be improved by selectively blocking the “preferential pathway”, diverting water to the previously unswept zones.
Known thermo-thickening compounds, such as polyethyleneglycol polymers (POE) described in EP0583814, would however be unsuitable for such a use, due to their low resistance to shearing.